Screen drum with screen tension adjustable axially and circumferentially

ABSTRACT

A screen drum apparatus and method of constructing it wherein a pair of attaching strips are secured to the opposite long side marginal portions of a rectangular screen formed with a multitude of very small openings therein, and the screen is mounted on a drum framework comprising a pair of main structural frame members and at least one ring-shaped adjusting frame member. The attaching strips are respectively fastened to the periphery of the adjusting frame member and one of the main frame members so that the screen is circumferentially attached to the drum framework to produce a screen drum in which the attaching strips are interposed between the screen and the drum framework. When the screen is mounted on the drum framework in this way, the screen is spread taut circumferentially of the screen drum, and the spread of the screen across the width of the screen drum can be adjusted by moving the adjusting frame member toward or away from the main structural frame members.

United States Patent Suzuki et al. l Aug. 5, 1975 [54l SCREEN DRUM WITH SCREEN TENSION 3 645 hl4 2/1972 McFurlane 355/3 ADJUSTABLE AXIALLY AND IGHUHSJ li/lQTl Frank. l r 4 r r i 355/3 CIRCUMFERENTIALLY Prmmm btummer-Norman G. Torchm l l Invcmorsl Shigeru Suzuki; Yasumori .4.\1\'is!uli[ lituml'ner.ludsOn R. Hightower Nagahara' hmh of Ylklhumill Altar-Hen Agml, or FirmT0wnsend and Townsend Yoshiharu Kagari, Tokyo, all of Japan [57] ABSTRACT |73| Assignce: Electroprint. lnc.. Cupertinu. Calif A screen drum apparatus and method of constructing I Filed: Dec- I7 973 it wherein a pair of attaching strips are secured to the opposite long side marginal portions of a rectangular [21 I Appl. No: 425,0[4 screen formed with a multitude of very small openings Reamd US Application Data therein, andthe screen mounted on a drum frame work comprising a pair at mam structural frame mem- [63] Continuation of Scri Nu. ltwts ll'lt), Aug. 3, l97l, bers and at [cast Om? ring shaped adjusting frame member The attaching strips are respectively fastened 3 1 U S C. 96 25} R to the periphery of the adjusting frame member and "j one of the main frame members so that the screen is {51 1 Int. LID .7 003g 5/00 circumfcremiuuy attached m the drum framework to Field of Search 433112 4 13 F g 1 produce a screen drum in which the attaching strips are interposed between the screen and the drum framework. When the screen is mounted on the drum ISM References (fled framework in this way the screen is spread taut cir' UNITED STATES PATENTS cumferentially of the screen drum, and the spread of 1,744267 t/l93ll Hamel [60/385 the screen across the width of the screen drum can be 3 (m4 592 10/1961 Norton i i t I l/ adjusted by moving the adjusting frame member to McFarlanc 4 4 r R rd or away from th main tructural frame mem. 332mm mum Catlin 4. 29 119 he 1453,71] 7/196) MucKcndrick 29/l48.4 D 3,625,604 11mm Pressman 355/3 5 Claims. 21 Drawing Figures PATENTEDAUB 51915 SW? 1 6538 0 1 FIG. l0 l6 new HJH HH ('8 [Li J INVENTORS swa /(w su PATENTEU AUG 51975 SHEET A TTORA/EV PATENTEU AUG 5x975 .EET

INVENTORS 5 U2 UK/ SCREEN DRUM WITH SCREEN TENSION ADJUSTABLE AXIALLY AND CIRCUMFERENTIALLY This is a continuation of application Ser. No. I68.I80. filed Aug. 3, I971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to drums and more particularly to an apparatus and method for tautly mounting a screen on a drum support.

When a screen member having a multitude of very small openings therein is formed into a drum shape, such as for use as a cylindrical sieve or a photosensitive screen drum. it is required to use a framework for supporting the screen because the screen itself lacks a structure for supporting itself. Particularly, in the case of a cylindrical sieve or photosensitive screen drum in which high accuracy and precision is required of the dimensions of the openings or meshes therein. it is necessary to spread the screen taut on the support without distorting the correct shape and varying the size of the openings or meshes of the screen.

This invention has as its object the provision of a screen drum producing method and apparatus which permits a screen to be spread readily, smoothly and correctly on its supporting framework so that screen drums of high quality can be produced at reduced cost.

SUMMARY OF THE INVENTION According to this invention. there is provided a screen drum wherein a screen is formed into a drum shape by attaching each of a pair of attaching strips to the opposite side marginal portions of the screen. and mounting it on a drum framework comprising a pair of main structural frame members and at least one ringshaped adjusting frame member attached to a structural frame member by a plurality of screws by bringing the attaching strips into engagement with the drum framework and securing the same thereto so that the screen may be attached to the drum framework to produce a screen drum in which the attaching strips are interposed between the screen and the drum framework. The screen drum produced by the method according to this invention can have its screen spread taut both circum ferentially and across the width of the screen drum. thereby permitting the production of a screen drum without distorting the shape and varying the size of the openings or meshes of the screen. The pair of main structural frame members and at least one ring-shaped adjusting frame member may be formed integrally to provide a drum framework in one piece.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. lultl are views in explanation of an electrophotographic printing method using a photosensitive screen formed with a multitude of very small openings or meshes therein:

FIG. 2 is a sectional view of one embodiment of the electrophotographic printing apparatus adapted to carry the clectrophotographic printing method into practice by using the photosensitive screen of FIG. I.

FIG. 3 is a plan view of a photosensitnc screen used for producing a photosensitive screen drum;

FIG. 4 is a plan view showing the manner in which a pair of attaching strips are secured to the screen of FIG. I;

(ill

FIG. 5 is a sectional view of a portion of FIG. 4 taken along the line VV thereof;

FIG. 6 is a sectional view showing the manner in which one of the attaching strips forming the pair is drawn inwardly after being secured to the screen;

FIG. 7 is a sectional view of a wire of the photosensi tive screen. a multitude of such wires being connected together to form the photosensitive screen;

FIG. 8 is a perspective view of a pair of ring-shaped frame members to which the screen is being attached;

FIG. 9 is a fragmentary side view of FIG. 8;

FIG. 10 is a side view showing the construction in part of a screen drum produced by the method according to this invention;

FIG. 11 is a fragmentary sectional view showing means for adjusting the spread of the screen across the width thereof;

FIG. 12 is a developed perspective view of another screen drum produced by a modification of the method according to this invention;

FIG. I3 is a fragmentary sectional view of the ringshaped structural frame member;

FIG. 14 is a fragmentary perspective showing the screen and attaching strip;

FIG. 15 is a front view showing the construction in part of the screen drum of FIG. 12;

FIG. I6 is a fragmentary perspective view showing another form of attaching strip for the screen;

FIG. I7 is a fragmentary sectional view showing the ring-shaped structural support member using the attaching strip of FIG. 16; and

FIG. I8 is a fragmentary sectional view of another screen drum produced by another form of the method according to this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The screen drums produced by the method according to this invention may have wide application. for example. as cylindrical sieves used in the chemical industry as well as photosensitive screens used in photocopying. It is to be understood. therefore, that the apparatus and method according to this invention can be carried into practice for producing screen drums used for many other purposes than for that which will be described.

This invention and its modifications will be explained with particular reference to its use with photosensitive screen drums. Photosensitive screen drums have particular utility in electrophotographic printing apparatus for carrying into practice electrophotographic printing methods using the principles summarized below.

In FIG. 1(a). there is shown a photosensitive screen IS which is produced by providing a photoconductive material layer 13 on one surface of an electrically conducting plate 12 formed with a multitude of very small openings 1] and an insulating material layer l4 on the other surface thereof. The electrically conducting plate I2 formed with the multitude of very small openings II may be prepared by connecting together fine wires of iron. steel. stainless steel. aluminum. zinc. copper. nickel or chrome into a screen of I00 to 300 mesh or by adhering a suitable metal on a plastic screen by vaporization in vacuum. The photoconductive material layer I3 may be provided by applying selenium. selenium sulfide. a dispersion of rinc oxide resin. a dispersion of cadmium sulfide. poly-N-vinyl carbazole or other organic photoconductive material. either as it stands or after increasing its photosensitivity. to one surface of the electrically conducting plate 12 by means of a spray gun or vaporization in vacuum. so that the layer may have a thickness of to 200 u. A suitable electrically insulating resin. such as tetrafluoroethylene resin or Teflon (trade name). or a suitable insulating paint may be used as a material for providing the insulating material layer [4.

The operation of producing a duplicate of an original by using the photosensitive screen 15 constructed as aforementioned in positive-to-positive or negativetonegative printing will be explained step by step.

First Step See FIG. 1(a)): Wire electrodes 16 and 17 on which a high voltage is impressed are arranged in face-to-face relationship with opposite surfaces of the photosensitive screen 15 for subjecting the latter to a corona discharge while the photoconductive material layer 13 is grounded. The photoconductive material layer 13 and insulating layer 14 are both uniformly charged in the same polarity Second Step (See FIG. lthl): An orignal 18 of transparent paper is arranged in face-to-face relationship with the photoconductive material layer 13 and exposed to light as indicated by a number of arrows. The

light transmitted through a non-image region 19 of the original 18 reaches the photoconductive material layer [3 but the light impinging on an image region 34 thereof is blocked thereby and does not reach the photoconductive material layer 13. Thus. the charge car ried by a region of the photoconductive material layer 13 corresponding to the non-image region disappears but the charge on a region of photoconductive material layer 13 corresponding to the image region 24 of the original [8 remains unaffected. so that an electrostatic latent image of the original 18 is formed on the photoconductive material layer 13. All the charge carried by the insulating material layer 14 remains unaffected.

Third Step (See FIG. I((') )1 An electrically insulating copy sheet 21. such as electrostatic recording sheet. in timately adhered to the back side of an opposite electrode plate is arranged in face to-face relationship with the surface of the photosensitive screen 15 on one surface of which an electrostatic latent image has been formed. and a wire electrode 22 is arranged in faceto face relationship with the other surface of the photosensitive screen 15. A voltage of opposite polarity to the voltage impressed on the electrodes 16 and I7 is impressed on the wire electrode 22. and a high voltage of opposite polarity to the voltage impressed on the wire electrode 22 is impressed on the wire electrode 22 is impressed on the opposite electrode plate 20. so as to subject the copy sheet 21 to a corona discharge while the electrically conducting plate 12 is grounded. Thus. an electrostatic latent image corresponding to the electrostatic latent image formed on the photosensitive screen 15 but oppositely charged thereto is formed on the copy sheet 2]. This is believed to be due to the fact that the movement of a corona discharge current produced by the electrode 22 is blocked by portions of the screen [5 which carry charges only on the insulating material layer but facilitated by portions of the screen 15 which carry charges on both the photoconductive material layer 13 and insulating layer l4 when such current is going to pass through the openings II in the screen [5. since the portions of the screen 15 carrying charges on the two layers l3 and I4 behave as if they carried no charge. resulting in the copy sheet 21 being charged by a current of corona ions that have passed through the openings ll.

Fourth Step (see FIG. l(d)): The electrostatic latent image formed on the copy sheet 21 as aforementioned is developed with a toner by a known process. ln this way. a toner image 23 corresponding to an image 24 of the original is produced on the copy sheet 2].

This duplicating method is suitable to positive-topositive or negative-to-negative printing. When it is desired to obtain a duplication in positive-to-negati e or negative-to-positive printing. one has only to repeat the aforementioned process by using a photosensitive screen which has no insulating layer provided thereon.

An electrophotographic copying apparatus will be described with reference to FIG. 2 which permits the continuous production of duplications of an original by using the photosensitive screen 15 arranged in drum shape to provide a photosensitive screen drum. in FIG. 2. there is shown a photosensitive screen drum 3] comprising a photosensitive screen (identical with the photosensitive screen l5 described above) which is produced by providing a photoconductive material layer and an insulating material layer on opposite surfaces of an electrically insulating plate formed therein with a multitude of very small openings. the photoconductive material layer being disposed on the outer side surface of the electrically conducting plate and the insulating layer on the inner side surface thereof. The photosensitive screen drum 31 is supported by a drive shaft 32 for rotation in the direction of the arrow u.

Electrically charging means 33 and 34 are disposed in the upper portion of FIG. 2 and arranged opposite each other with respect to the photosensitive screen of the photosensitive screen drum 31. High voltages of the same polarity are impressed on the charging means 33 and 34 so as to subject the photosensitive screen drum 3] to a corona discharge to uniformly charge opposite surfaces ofthe photosensitive screen as the drum 3] rotates.

Upon completion of charging. the photosensitive screen ofthe photosensitive screen drum 3] is exposed. through a projection lens 35 and a slit member 36 disposed on the left side of HO. 2 and in a slit system to an optical image of an original 37 moving in the direction of the arrow h in synchronism with the movement of the photosensitive screen drum 3]. Any other exposing means may be used.

The photosensitive screen on the photosensitive screen drum 3| on which an electrostatic latent image has been formed by the aforementioned process is then passed between charging means 38 disposed inwardly of the lower portion of the drum 3! and an opposite electrode plate 39 disposed outwardly thereof in FIGv 2.

An insulating copy sheet 40 is delivered to the opposite electrode plate 39 at a rate equal to the peripheral velocity ofthe drum 31 and in synchronism with the rotation of the drum 3]. and com eyed in the direction of the arrow c while being held intimately on the plate 39 by the negative pressure ofthe latter. During the movement of the copy sheet 40. a high voltage of opposite polarity to the voltages impressed on the charging means 33 and 34 is impressed on the charging means 38 and a bias \oltagc of opposite polarity to the voltage impressed on the charging means 38 is impressed on the opposite electrode plate 39. so that the copy sheet 40 being conveyed is subjected to a corona discharge,

Thus. an electrostatic latent image is formed on the copy sheet 40 which corresponds to the electrostatic latent image on the photosensitive screen of the drum 31 but which is oppositely charged thereto.

The copy sheet 4|) on which an electrostatic latent image has been formed is delivered by a pair of conveyor rollers 41 to a developing solution tank 42 in which several rows of guide fins 43 and 44 are provided in the upper and lower portions. The copy sheet 40 is guided by these f ns and discharged from the system to outside through a pair of squeeze rollers 45. It is to be understood that the electrostatic latent image on the copy sheet 40 may be developed by any other known dry developing method than the wet developing method described above.

The photosensitive screen drum used in the aforementioned electrostatic copying apparatus is produced as described previously, by spreading a screen with a multitude of very small openings on a drum framework.

The present invention will be explained in detail with reference to FIGS. 3 to II. In FIG. 3, there is shown a screen 51 which may be to 60 pt thick, and produced by connecting fine wires of stainless steel together at a rate of ISO to 250 wires per inch in screen form and then pressing the product. This screen 5] may be made into a photosensitive screen 54 (see FIG. 7). by applying a photoconductive material layer 52 and an insulat ing layer 53 as described previously on opposite surfaces of the screen 5]. The steps of the method according to this invention will be described with reference to embodiments using the screen 51.

Firstly. attaching strips 55 ad 56 made of bronze or the like are each secured. as by soldering. to the opposite lateral marginal portions of the underside of the screen 5| lengthwise thereof. FIG. 5 shows in section the attaching strip 55 soldered to the screen 5| at 57. The screen 5| with attaching strips 55 and 56 secured thereto is mounted in a manner presently to be described on a pair of ring-shaped adjusting frame members 60 and 6|. which are connected to a pair of main structural frame members 58 and 59 as shown in FIG. 8. The structural frame members 58 and 59 which may also be ring-shaped. are firmly connected together by rigid support rods 62. 63 and 64. and may be made of a suitable metal of relatively low resilience having high resistance to forces exerted thereon circumferentially but of relatively low resistance to forces exerted on the end surfaces thereof. The adjusting frame members 60 and 6| are connected to the structural frame members 58 and 59 respectively by a number ofscrews 65 which are loosely connected to the frame members 58 and 59. Three recesses may be formed in the peripheral edges of each of the frame members 60 and 6] for receiving the support rods 62. 63 and 64 therein. Initially. the adjusting frame members 60 and 61 are not firmly secured but are movable axially of the support rods 62. 63 and 64 by adjusting the screws 65.

A plurality ofthreaded openings 66 are formed in the peripheral edge of each of the adjusting frame mem bers 60 and 6|. and a plurality of threaded openings 67 corresponding in position to the threaded openings 66 are formed in each ofthc attaching strips 55 and 56 secured to the screen SI. The screen 51 may be spread on a table or other surface with the attaching strips 55 and 56 facing upwardly and mounted on the adjusting frame members 60 and 6| by bringing the threaded openings 66 into index with the corresponding threaded openings 67 and threadably inserting screws 68 (see FIG. 9) into the openings 66 and 67 to firmly attach the screen SI to the frame members and 6]. In this screen attaching operation. the support rods 62, 63 and 64 are left uncovered with the screen 5].

When the screen 5| is attached to the frame members 60 and 61 as aforementioned. the upper surface of the screen SI is disposed outwardly ofthe outer peripheral surface ofthe resultant drum-shaped member. The screen 5| arranged in drumshape is disposed outwardly of the attaching strips 55 and 56. so that the screen SI is subjected to a tensile force which stretches the portion of the screen 5] which is disposed outwardly of the center line (I. As a result. the screen 5] is suitably stretched circumferentially 0f the drumshapcd member.

In securing the attaching strips 55 and 56 to the adjusting frame members 60 and 61, an error which might otherwise occur in attaching the screen 51 to these members 60 and 61 can be obviated or minimized if the center part of the screen 5] is first connected to the frame members 60 and 6] and then successive portions are secured till finally the opposite end portions are connected. If the screen 51 is attached to the adjusting frame members 60 and 6| in the manner described. then the drum-shaped member produced substantially assumes the form of a screen drum. though the screen 5] may be somewhat loose across the width thereof. If any position ofthe screen 5] of the drumshapcd mem ber produced in this way is loose across the width of the screen. then the screw or screws at such portion of the screen 51 are turned to move the adjusting frame member 60 toward the structural frame member 58. Since the ring-shaped frame member 6| offers a relatively low resistance to a force exerted on an end surface thereof as described previously. the portion of the frame member 6| corresponding to the loose portion of the screen 5] moves in the direction of the arrow d as shown in FIG. I]. [t is thus possible to locally adjust the spread of the screen 5|.

If the screws 65 are adjusted in all the portions of the structural frame members 58 and 59 by taking the spread of the screen 5| on its entire surface. then it is possible to obtain an optimum spread of the screen 51 so that the screen 5] is mounted taut on the frame members without being tightened or slackened. When this condition is obtained. the screen 51 and ring shaped frame members 60 and 6| pull each other in tension and are positively supported by the structural frame members 58 and 59.

In the aforementioned step. if the attaching strips 55 and 56 are drawn inwardly as shown in FIG. 6 by rotation after being secured to the screen 51. it is possible to prevent the soldered portion 57 from being exposed to view. Besides. the screen 5| can be supported by the adjusting frame members more positively if the screen 51 is secured to the ring-shaped frame members 60 and 6| with opposite side portions of the screen SI being folded into contact with the undersides of the strips. in mounting the screen 5] on the frame members 60 and 61.

Modifications of the photosensitive screen drum and the method of producing it according to this invention will be described with reference to FIGS. II to I8. In FIG. 12. a pair of sturdily built structural frame members l0l and I02 are disposed in face-to-face relationship and connected to each other by rigid connecting rods I03, I04 and 105 which are attached to arcuatc portions of the structural frame members I01 and I02 which are slightly smaller than semicircular portions thereof. This arrangement is sufficiently stable to sc curely support the photosensitive drum as a whole. The connecting rods I03, 104 and 105 are lopsidedly connected to the frame members 101 and 102 as aforementioned in order that the screen 113 may have the greatest possible effective area.

The structural frame member 101 is formed on its outer peripheral surface with a circumferentially dis posed groove 101a ofa small width. and oppositely fac ing cutouts 101!) and 101a are formed on a portion of the outer peripheral surface of the member 101 dis posed inwardly of the groove 101a in positions which correspond to the positions in which the connecting rods 103 and 105 are secured to the member 101. A stopper 106 having a pin 106a is adjustably mounted in the cutout 101!) by a screw (not shown), and a pin 107 is attached to the other cutout 1016.

On the opposite side, a ring-shaped adjusting frame member 108 of relatively small width. formed with oppositely facing cutouts 108a and l08h in positions in its outer peripheral surface corresponding to the positions in which the connecting rods 103 and 105 are disposed. is arranged inwardly of the structural frame member 102. The adjusting frame member 108 is adjustably connected to the structural frame member 102 by a plurality of equidistantly-spaced adjusting bolts 109. Cutouts are formed in positions on the outer peripheral surface of the ring-shaped adjusting frame member 108, corresponding to the positions in which the con necting rods 103 and 105 are disposed, for receiving the connecting rods therein. A stopper 110 having a pin 1100 is adjustably mounted in the cutout 10811 of the ring-shaped adjusting frame member 108 by a screw 111 (see FIG, 13) in the same manner as the stopper 106 is mounted in the cutout 1011:. Similarly. a pin 112 is attached to the cutout 108/; in the manner of pin 107 in cutout 1011'.

A screen 113 produced in the same manner as described previously is mounted on the frame members 101 and 108 in a process presently to be described in one modification of the apparatus and method according to this invention, so as to provide a screen drum. Opposite end marginal portions of the screen I13 spaced apart lengthwise of the screen from each other are folded twice or three times to form folded portions 113a and 113k. and attaching strips I14 and 115 of small width which may be made of metal are secured as by soldering. to opposite side marginal portions of the screen 113 spaced apart across the width of the screen from each other. The attaching strips 114 and 115 which have a length slightly greater than the length of the screen 113 are slightly bent at their outer mar ginal portions to form engaging portions 114a and l I51! (See FIG. 14).

Openings H4!) and 1141' and I]; and 1150 are formed on opposite end portions of the attaching strips 114 and 115. respectively. for recei\ing the pins 106a and 107. and 110a and H2. rcspcctnely The screen 113 is mounted on the structural frame member 101 and ring'shapcd adjusting frame member 108 (see FIG 13) by first inserting the pins I07 and 112 in the opeir ings lI-It' and llSt' and then fitting the engaging por tions 114a and 115a in the circumferential grooic I0ltl in the structural frame member I01 and on the outer edge of the outer peripheral surface of the frame member I08 respectively.

After the screen 113 is mounted on the structural frame member 101 and ring-shaped adjusting frame member 108, the pins 106a and 11011 are inserted in the openings I14): and respectively and the positions of the stoppers 106 and I10 are adjusted as by threading the screw 111 into the cutout 108a. so as to spread the screen taut lengthwise thereof. The screen is thus spread taut lengthwise thereof on the frame members 101 and 108 by the difference in tensile force exerted on its outer peripheral surface and inner peripheral surface.

On the other hand. the screen 113 can be spread taut across the width thereof by moving the adjusting bolts 109 so as to adjust the position of the ring-shaped adjusting frame member 108 with respect to the frame member 10] thereby spreading the screen 113 across its width (see FIGv 15).

The screen drum produced in the manner described above is rotatably supported. when the screen drum is a photosensitive screen drum. by rollers I16, I17, 118. ll). I20 and 121 shown in the dash-and-dot or broken lines in FIG. 12. The rollers I16 and 117 are maintained in pressing engagement with the outer peripheral surface of the structural frame member 101 and the roller 120 is maintained in pressing cngagment with the inner peripheral surface thereon so as to hold the frame member 101 therebetween. Similarly. the rollers I18 and 119 are maintained in pressing engagement with the outer peripheral surface of the frame member 108 and the roller 12] is maintained in pressing en gagement with the inner peripheral surface thereof so as to hold the member 108 thcrebetween. The screen drum can be held against movement axially thereof by rollers (not shown) maintained in the engagement with end surfaces ofthe structural frame members 101 and I02. A relief cam 122 of crescent shape is shown provided on the inner end surface of the structural frame member 101. and a gear 123 is shown mounted on the outer end surface thereof to satisfy other requirements of designing.

In the modification of the apparatus and method according to this invention described above. the structural frame members [0] and 102 are shown and described as ringshaped or annular in shape. The invention is not limited to this specific form of the frame members 101 and 102, and members of any form may be used as desiredv The structural frame member 101 is shown as being integrally formed with a ring-shaped adjusting frame member. However. the frame member 101 and the adjusting frame member may be formed separately in two pieces and connected together in combination as are the other structural frame member I02 and the adjusting support member 108.

The bent outer marginal portions of the attaching strips serving as engaging portions have a height which is greater than the thickness of the attaching strips. However. since the ring-shaped frame member has a large diameter. the screen can be readily mounted on the frame members.

FIG. I6 shows an alternate form of engaging portion wherein a number of pins 124 attached to an attaching strip I23 secured to a screen 122 serve as engaging portions. The pins 124 are adapted to be rcceiicd in corresponding openings 125a formed in a ring-shaped ad justing frame member 125 (see HQ 17) when the screen 122 is mounted on the frame members, The engaging portions of this form are effective to readily produce a screen drum by mounting a screen on the frame members. An opening [23a formed at an end portion of the attaching strip [23 serves the same purpose as the openings 11411. I 14c. llSh and H50 formed in the attaching strips 114 and HS. An end portion of the screen 122 is folded like the screen M3 to provide a folded portion 122.

FIG. 18 shows another modification ofthe apparatus and method according to this invention for producing a screen drum, In FIG, IS. a ring-shaped adjusting frame member 127 is provided outwardly of a main structural frame member 126 so that a screen 128 is mounted on the ring-shaped adjusting frame member 127. In this modification. screws 129 for moving the frame member [27 toward or away from the main frame member 12: threadably extend through the frame member 127 into engagement at their front end portion in openings formed in the frame member 126. When it is desired to spread the screen I28 taut across the width thereof. the screws 129 are turned to move the adjusting frame member 127 outwardly away from the main frame member [26. It is to be understood that according to this invention any other means than the screws I29, such as means using springs and pins, for example. may be used for moving the adjusting frame member 127 toward or away from the main frame member 126.

The apparatus and method according to this invention and the modifications thereof which are shown and described herein may be used for producing a screen drum comprising a screen made of a synthetic resinous material as well as stainless steel of aforementioned. The screen drum produced by this invention and the modifications thereof can be used not only in electrophotographic copying but also in any other fields in which a screen drum formed with a multitude of very small openings in its outer periphery is needed. In case no adjustments of the spread of the screen across the width thereof are required. the structural frame members and ring-shaped frame members may be formed integrally in one piece as a drum framework. The drum framework may be a cylindrical member formed with openings therein.

What is claimed is:

l. A photosensitive screen drum for use in noncontact electrostatic printing comprising:

a. two main frame membersi b. spacing means rigidly connecting said main frame members in spaced face-toface relationship to form a drum framework;

c. a screen member having a photoconductive material layer on one side thereof;

d. attaching strips secured to each of two opposite marginal portions of said screen member and having a plurality of engaging means thereon;

e. at least one circular adjusting frame member;

f. means spaced on the outer peripheries of said adjusting frame member and one of said two main frame members and cooperating with said engaging means for fastening said attaching strips respectively to said adjusting frame member and to one of said two main frame members whereby said screen may be tensioned circumferentially; and

g means for adjustably connecting said adjusting frame member to the other of said two main frame members for axial movement with respect to the drum framework whereby said screen member may be adjustably tensioned across the width of the screen drum.

2. A screen drum as in claim 1 in which said screen is provided on the other surface thereof with an insulating material layer.

3. A screen drum as in claim I wherein said engaging means comprises screw means and said cooperating means comprises receptacles for said screw means. so that in circumferential tension of said screen member may be adjusted 4. A screen drum as in claim 3 wherein said screw means are positioned adjacent the opposite ends of said attaching strips.

5. A screen drum as in claim I further comprising bent portions on the outer edges of said attaching strips for engaging the outer end surfaces of said frame members.

l k *4 k 

1. A PHOTOSENSITIVE SCREEN DRUM FOR USE IN NONCONTACT ELECTROSTATIC PRINTING COMPRISING. A. TWO MAIN FRAME MEMBERS, B. SPACING MEANS RIGIDLY CONNECTING SAID MAIN FRAME MEMBERS IN SPACED FACE-TO-FACE RELATIONSHIP TO FORM A DRUM FRAMEWORK. C. A SCREEN HAVING A PHOTOCONDUCTIVE MATERIAL LAYER ON ONE SIDE THEREOF D. ATTACHING STRIPS SECURED TO EACH OF TWO OPPOSITE MARGINAL PORTIONS OF SAID SCREEN MEMBER AND HAVING A PLURITY OF ENGAGING MEANS THEREON, E.AT LEAST ONE CIRCULAR ADJUSTING FRAME MEMBER, F. MEANS SPACED ON THE OUTER PERIPHERIES OF SAID ADJUSTING FRAME MEMBER AND ONE OF SAID TWO MAIN FRAME MEMBERS AND COOPERATING WITH SAID ENGAGING MEANS FOR FASTENING SAID ATTACHING STRIPS RESPECTIVELY TO SAID ADJUSTING FRAME MEMBERS AND TO ONE OF SAID TWO MAIN FRAME MEMBERS. WHEREBY SAID SCREEN MAY BE TENSIONED CIRCUMFERENTIALLY AND G.MEANS FOR ADJUSTABLY CONNECTING SAID ADJUSTING FRAME MEMBER TO THE OTHER OF SAID TWO MAIN FRAME MEMBERS FOR AXIAL MOVEMENT WITH RESPECT TO THE DRUM FRAMEWORK WHEREBY SAID SCREEN MEMBER MAY BE ADJUSTABLY TENSIONED ACROSS THE WIDTH OF THE SCREEN DRUM.
 2. A screen drum as in claim 1 in which said screen is provided on the other surface thereof with an insulating material layer.
 3. A screen drum as in claim 1 wherein said engaging means comprises screw means and said cooperating means comprises receptacles for said screw means, so that in circumferential tension of said screen member may be adjusted.
 4. A screen drum as in claim 3 wherein said screw means are positioned adjacent the opposite ends of said attaching strips.
 5. A screen drum as in claim 1 further comprising bent portions on the outer edges of said attaching strips for engaging the outer end surfaces of said frame members. 